Do you avoid eating soy foods because you’re worried they’ll give you breasts? You’re not alone! Many men avoid soy foods like soy milk, tofu, and tempeh even though these foods are a high-quality plant protein. However, it appears that the notion of getting “man boobs” is just a myth. Here’s how this myth got started, and what the studies really show.

Where Did Soy’s Link to Man Boobs Originate?

Because soy foods are rich in isoflavones (commonly referred to as phytoestrogens) many folks looked at the word “estrogen” and believed soy to have a feminizing effect. In 2009, an article published in a men’s magazine really raised the issue. The article focused on animal studies and a recent case report about an older gentleman who developed feminizing effects – like erectile dysfunction, development of breasts, and loss of libido – both linked eating soy with very high estrogen levels that soy supposedly caused. To make things worse, a 2008 study found that soy intake was associated with a lower sperm concentration among 99 male partners of sub-fertile couples.

The problem with the 2009 men’s magazine article is that it did not emphasize “that the older man who developed feminizing effects consumed 3 quarts of soymilk per day,” explains Mark Messina, PhD, MS Adjunct Associate Professor, Dept. of Nutrition School of Public Health, Loma Linda University and Executive Director at the Soy Nutrition Institute. Messina says that “if that soymilk was made from whole soybeans, which was almost certainly the case, isoflavone intake would have been approximately 300 mg per day, which is 8-9 times higher than the isoflavone intake of older Japanese men.” 

This type of article really goes to show that you need to look into the actual study before always believing the headlines.

What the Research Says

Sharon Palmer, RDN, The Plant-Powered Dietitian explains that soy does not cause development of breasts in men. “Research shows that moderate soy intake does not lead to feminization in men, and indeed countries in Asia that consume large amounts of soy on a regular basis do not demonstrate concerns in this area. This is a largely misunderstood concern, with much hype over the internet and non-science based information,” says Palmer.

In addition, Messina links much research to where soy had no significant effects on feminization of men. “A meta-analysis published in 2010 that included 32 studies and 36 treatment groups that found there were no significant effects of soy protein or isoflavone intake on levels of total testosterone, sex hormone binding globulin, free testosterone or the free androgen index,” explains Messina, quoting a study from the journal Fertility and Sterility. Subsequently many more studies disproving the connection between eating soy and the development of breasts and other feminine features followed.

Why Eat Soy?

In a plant-based world, soy is a high-quality protein that can help you get more protein. According to Palmer soy “is very similar in terms of its amino acid profile to animal proteins.” Soy also has an array of nutrients including fiber, vitamins, minerals, antioxidants, phytochemicals, and anti-inflammatory action.

The safe recommendation for soy is up to two servings of whole soy foods per day; some studies even show up to three servings per day. Examples of one serving are 1/2 cup soybeans, tofu, or tempeh, or 1 cup soy milk. 

Bottom Line

Soy foods like tofu, edamame, tempeh, and soy milk are a high quality plant protein that can help build muscles, not boobs.

Toby Amidor is the owner of Toby Amidor Nutrition and best-selling author of Smart Meal Prep for Beginners, The Easy 5-Ingredient Healthy Cookbook, The Healthy Meal Prep Cookbook, and The Greek Yogurt Kitchen.